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United States Patent |
5,290,313
|
Heldreth
|
March 1, 1994
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Offset prosthetic stem extension
Abstract
A modular prosthesis system which includes a modular stem extension which
has an offset between its attachment point to the prosthesis base portion
and the main body of the stem. The stem extension can be attached in a
selected orientation with respect to the base portion, thus enabling the
main body of the stem to be positioned in any of one of a plurality of
orientations with respect to the base portion.
Inventors:
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Heldreth; Mark A. (Mentone, IN)
|
Assignee:
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Zimmer, Inc. (Warsaw, IN)
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Appl. No.:
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979978 |
Filed:
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November 23, 1992 |
Current U.S. Class: |
623/20.15 |
Intern'l Class: |
A61F 002/38 |
Field of Search: |
623/18,20,23
|
References Cited
U.S. Patent Documents
4790854 | Dec., 1988 | Harder et al. | 623/20.
|
4822365 | Apr., 1989 | Walker et al. | 623/20.
|
4822366 | Apr., 1989 | Bolesky | 623/20.
|
4834081 | May., 1989 | Van Zile | 128/92.
|
4936853 | Jun., 1990 | Fabian et al. | 623/20.
|
4950297 | Aug., 1990 | Elloy et al. | 623/20.
|
4950298 | Aug., 1990 | Gustilo et al. | 623/20.
|
4959071 | Sep., 1990 | Brown et al. | 623/20.
|
4963155 | Oct., 1990 | Lazzeri et al. | 623/23.
|
4985037 | Jan., 1991 | Petersen | 623/20.
|
5002578 | Mar., 1991 | Luman | 623/23.
|
5071438 | Dec., 1991 | Jones et al. | 623/18.
|
5123928 | Jun., 1992 | Moser | 623/20.
|
5133760 | Jul., 1992 | Petersen et al. | 623/20.
|
5133763 | Jul., 1992 | Branemark | 623/18.
|
5152796 | Oct., 1992 | Slamin | 623/20.
|
Other References
Zimmer, Inc.-Catalog pp. A118,A121--Miller/Galante Total Knee--1987
catalog.
Zimmer, Inc.--Catalog pp. A141,A143--MG II Total Knee System--1991 catalog.
Zimmer, Inc.--Catalog pp. A169,A171--Insall/Burstein II Modular Knee
System--1991 catalog.
|
Primary Examiner: Isabella; David J.
Assistant Examiner: Brittingham; Debra S.
Attorney, Agent or Firm: Geringer; Margaret L.
Claims
I claim:
1. A modular prosthesis system comprising a prosthetic base portion having
a surface for positioning adjacent to a corresponding bone, the base
portion having a base mounting means thereon, and a stem extension for
insertion into a cavity in a bone, the stem extension having a stem
mounting means for mounting the stem extension to the base mounting means,
and the stem extension further having an elongated stem portion connected
to the stem mounting means by a connection portion, and wherein the stem
mounting means has a first central longitudinal axis and the elongated
stem portion has a second central longitudinal axis substantially parallel
to the first axis, but which is spaced apart therefrom to provide an
offset therebetween.
2. The system of claim 1 wherein the stem mounting means is radially
adjustable in cooperation with the base mounting means so that the second
axis of the elongated stem portion can be oriented in any one of a
plurality of radial orientations with respect to the first axis.
3. The system of claim 2 wherein the stem extension is releasably fixed to
the base portion in the selected orientation.
4. The system of claim 1 wherein the connecting portion includes a lower
transition surface which crosses the first axis.
5. The system of claim 4 wherein the lower transition surface crosses the
first axis substantially perpendicularly.
6. The system of claim 4 wherein the lower transition surface crosses the
first axis at an angle which is between about 5 and 90 degrees.
7. The system of claim 4 wherein the lower transition surface is a curved
surface which crosses the first axis.
8. The system of claim 1 wherein the base mounting means includes a recess
therein, and wherein the stem mounting means includes an extending pin for
mating with the recess.
9. The system of claim 8 wherein the recess and the pin each include mating
tapered surfaces to provide a secure mating interlock therebetween.
10. The system of claim 8 wherein the pin extends from a platform on the
stem extension and wherein a raised wall also extends from the platform,
such that the raised wall is spaced apart from the pin.
11. The system of claim 10 wherein the recess in the base mounting means is
formed in an extension member on the base portion and wherein the
extension member has a generally cylindrical outer surface and wherein the
raised wall on the stem extension has a generally curved inner surface to
complement the outer surface of the extension member and which partially
surrounds the extension member when the stem extension is connected to the
base portion.
12. The system of claim 1 wherein the base mounting means includes an
extending pin, and wherein the stem mounting means includes a recess
therein for mating with the pin.
13. The system of claim 1 wherein the system includes a plurality of base
portions of varying sizes and a plurality of stem extensions of varying
sizes, such that any one of the stem extensions can be selectively
attached to any one of the base portions.
14. The system of claim 13 wherein the plurality of stem extensions are
sized to provide a plurality of different offsets by varying the distance
between the first and second axes.
15. The system of claim 1 wherein the connecting portion includes an upper
transition surface which provides a cut-out portion positioned axially
above the elongated stem portion.
16. The system of claim 1 wherein the connecting portion includes an upper
transition portion which extends the connecting portion to at least
partially fill an area positioned axially above the elongated stem
portion.
17. The system of claim 1 wherein the stem mounting means is selectively
positionable in a plurality of orientations with respect to the base
mounting means, so that the second axis can be selectively oriented in a
plurality of positions with respect to the first axis and with respect to
the base portion.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a modular prosthetic implant system. In
particular, this invention relates to such a system which includes modular
stem extensions.
While this invention is particularly suitable for modular tibial prosthesis
components having modular stem extensions, the features of this invention
could be adapted, as appropriate, to other prosthetic components which
utilize modular stem components.
It is well known in the art to utilize modular stem extensions. The
following patents disclose the use of modular stem extensions which are
straight and aligned with the attachment mechanism: U.S. Pat. Nos.
4,936,853; 4,950,298; and 4,959,071, while U.S. Pat. No. 4,822,366
discloses both a straight modular stem and a modular stem having a bowed
or curved end portion.
In addition, U.S. Pat. No. 4,834,081 discloses a modular stem extension
which is angled realtive to the prosthesis; while the following patents
each disclose modular stems in which the modular angled stem can be
attached to the prosthesis base in a plurality of positions to selectively
vary the orientation of the angled stem relative to the prosthesis base:
U.S. Pat. Nos. 4,822,365; 4,985,037; 5,133,760; 5,152,796.
In addition, U.S. Pat. No. 4,950,297 is noted of related interest. It
discloses a control peg 21 which is fitted between the tibial and meniscal
components. The control peg includes superior and inferior axial portions
which are connected by a collar and are laterally offset from each other.
The control peg controls subluxation and/or rotation of the meniscal
component with respect to the tibial component. This patent is cited to
point out the offset relationship of the control peg. However, it is noted
that the control peg of this patent is not a stem extension, and it is
utilized in a different manner and for a different purpose than the offset
stem extension of the present invention.
OBJECTS OF THE INVENTION
A principal object of this invention is to provide a modular stem extension
which has an offset between its attachement point to the prosthesis base
portion and the main body of the stem.
A further object of the invention is to provide such an offset stem
extension which can be attached in a selected orientation with respect to
the base portion, thus enabling the main body of the stem to be positioned
in any one of a plurality of orientations with respect to the base
portion.
Another object of the invention is to provide a modular stem extension in
which the amount of mediolateral offset can be varied depending upon the
selected orientation of the stem extension to the base plate.
A still further object of the invention is to provide a modular offset stem
extension which can be used with either right or left implant components.
SUMMARY OF THE INVENTION
The present invention provides a modular prosthesis system including a
prosthetic base portion and a stem extension which is to be mounted to the
undersurface of the base portion. The axis of the main body of the stem or
the elongated stem portion of the stem extension is offset or spaced from
the axis of the mounting portion of the stem extension.
As noted above, while the features of this invention could be adapted to
various stemmed prosthetic components, it is particularly suitable for use
with modular tibial prosthesis components, although it is not limited
thereto. The anatomy of the human tibia is quite variable with respect to
the position of the intramedullary canal relative to the mediolateral
edges of the proximal tibia. A stem which is centrally located on the base
portion or base plate could interfere with the lateral trbial cortex as a
surgeon attempts to center the tibial plate on the proximal cut tibia.
There are some patients in which the intramedullary canal is not centrally
located relative to the peripheral edges of the proximal tibia. In such
cases, the option for an offset stem extension, such as that of the
present invention could be a beneficial option. This option could also
allow the same base portions or base plates to be used with patients
utilizing various styles of stem extensions, including the offset style of
the present invention, as well as other known sytles of stem extensions
such as straight, bowed, or angled stem extensions.
BRIEF DESCRIPTION OF THE DRAWINGS
These features and objects of the invention, as well as others, will become
apparent to those skilled in the art by referring to the accompanying
drawings:
FIG. 1 is a perspective view of a modular tibial prosthesis assembly in
accordance with the present invention;
FIG. 2 is an exploded front view of the base portion and stem extension of
the tibial prosthesis of FIG. 1;
FIG. 3 is a top end view of the stem extension taken along lines 3--3 of
FIG. 2;
FIG. 4 is a cross-sectional view of the stem extension taken along lines
4--4 of FIG. 2;
FIG. 5 is a cross-sectional view of the stem extension taken along lines
5--5 of FIG. 2;
FIGS. 6,7, and 8 are front views of alternate embodiments of the stem
extension;
FIG. 9 is a schematic representation of a plurality of various selectable
positions of the axis of the stem extension relative to the fixed axis of
the mounting or attachment portion.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1-9 illustrate particularly advantageous embodiments of the offset
prosthetic stem extension of the present invention. The invention will be
described with reference to a modular prosthetic tibial component 50;
however, it is understood that it is not limited thereto.
The modular tibial component of FIG. 1 includes a base plate or base
portion 10, with a modular stem extension 1 attached thereto. The base
portion also includes an articular surface or additional portion 20 which
may also be modular. Such modular additional portions are well known in
the art, and as such, this portion 20 may be secured to the base portion
by any suitable attachment mechanism. Typically, the articular surface 20
of a tibial component 50 is made of an ultra high molecular weight
polyethylene material; however, any suitable material may be used.
Accordingly, the base portion 10 and stem extension 1 are typically
manufactured from a metal material such as a cobalt-chrome alloy or a
titanium alloy; however, any suitable material may be utilized. Also, any
appropriate manufacturing methods may be utilized for these parts.
As seen in FIGS. 2-5, the base portion 10 has an undersurface 11 with a
base mounting portion 12 thereon. The stem extension 1 has a stem mounting
portion 2 for mounting the stem extension 1 to the base mounting portion
12. The stem extension 1 also includes an elongated stem portion 3
connected to the stem mounting portion 2 by a connecting portion 4. The
stem mounting portion has a first axis "A" and the stem portion 3 has a
second axis "B" which is substantially parallel to the first axis "A," but
which is spaced apart therefrom to provide a fixed offset "0" or fixed
distance between the parallel axes "A" and "B."
The stem mounting portion 2 is radially adjustable in cooperation with the
base mounting portion 12, so that the second axis "B" of the elongated
stem portion 3 can be oriented in any one of a plurality of radial
orientations with respect to the first axis "A." This can be seen by
looking at the schematic representation of the tibial component 50 shown
in FIG. 9. Axis "A" has a fixed orientation relative to the base portion
10 (which may be attached to additional portion 20), while a plurality of
radial orientations for the second axis "B" are shown, such as by "B1,"
"B2," "B3," "B4," "B5." The surgeon would select the desired position for
axis "B" relative to the base portion 10, and then the stem extension 1
can be releasably fixed to the base portion 10 in the selected
orientation.
The amount of mediolateral offset (the offset in the mediolateral
direction) can be varied depending upon the selected orientation of the
stem extension 1 relative to the base plate 10. For example, as shown in
FIG. 9, if the location for the second axis is "B5," the mediolateral
offset would be "ML1," while if the location for the second axis is
"B4,"the mediolateral offset would be "ML2" which is a greater
mediolateral offset than "ML1." Thus, for a given stem extension 1, while
the offset "0" or the actual distance between the axes "A" and "B" is
fixed or constant, the mediolaterial offset may vary as the orientation of
axis "B" varies relative to the base portion 20 and fixed axis "A." The
mediolateral offset may preferably be about 3 to 7 mm, although other
offset distances may be selected, as desired.
The base mounting portion 12 may include an extension member 42 with a
recess 43 therein. The stem mounting portion 2 includes an extending pin
33 for mating with recess 43. The recess 43 and pin 33 may each include
mating tapered or conical surfaces to provide a secure mating interlock
therebetween. This conical attachment enables the stem extension 1 to be
attached in any selected radial orientation. Also, additional securing
features could be utilized to further secure this tapered connection, such
as a screw (not shown) which could connect through the base portion 10
into the pin 33 of the stem extension 1. Such screws are known in the art
to be used on existing straight stem extensions. It is noted that other
suitable attachment mechanisms could be utilized. For example, the
attachment mechanism could be keyed (not shown) to provide a specific
limited number of relative stem positions rather than the unlimited number
of radial positions possible with the smooth conical surfaces shown.
The pin 33 extends from a platform 34 on stem extension 1. As shown in the
embodiment of FIG. 2 and 3, a raised wall 35 is spaced apart from pin 33.
The extension member 42 extending from undersurface 11 of base portion 10
has a generally cylindrical outer surface. The raised wall 35 on stem
extension 1 has a generally curved inner surface 36 to complement the
outer surface of the extension member 42. Raised wall 35 partially
surrounds extension member 42 when the stem extension 1 is connected to
the base portion 10.
Alternate embodiments of extension members 1 are shown in FIGS. 6,7, and 8.
For example, while the stem extension of FIG. 2 includes raised wall 35,
the embodiments of FIGS. 6,7, and 8 do not. Thus, with the embodiment of
FIG. 2 there would be no unfilled space directly above the platform 34
when the stem extension is connected to base portion 10. In comparison,
when the embodiment of FIG. 6 is attached to base portion 10, a space
directly above the platform 34 (which is not covered by extension member
42) and below undersurface 11 would potentially need to be filled with
bone chips or bone grafting material to fill this space, since use of
typical surgical procedures would call for reaming or rasping or tamping a
suitably shaped hole in the bone to accommodate the correspondingly shaped
stem extension 1.
It is noted that the embodiments of FIGS. 6 and 7 are the current preferred
embodiments of the present invention. However, the embodiments of FIGS. 2
and 8 are also suitable alternatives. It is understood that other
variations in design could be comtemplated in keeping with the features of
the present invention.
As shown in FIGS. 1,2, and 5, flutes 6 may be provided in the elongated
stem portion, if desired.
As shown in the embodiment of FIG. 8, the stem mounting portion 2 may
utilize a conical recess 83 rather than the extending pin 33 of the
embodiments of FIGS. 2,6, and 7. When the stem mounting portion is a
conical recess 83 as in FIG. 8, then the corresponding base mounting
portion would be a conical pin (not shown) extending from the undersurface
11 of base portion 10.
Also, the connecting portion 4 includes a lower transition surface 7 and an
upper transition surface 8. The contours of these upper and lower
transition surfaces vary with the shape of the connecting portion 4. For
example, in the embodiment of FIG. 8, the upper transition surface 8
provides a cutout portion positioned in line above the elongated stem
portion. When using such an embodiment in surgery, this cutout portion
would need to be filled with bone chips or bone grafting material to fill
this space in the bone opening. Alternatively, the upper transition
portion 8 of FIGS. 2,6, and 7 extends the connecting portion to fill in
the area positioned in line above the elongated stem portion. In FIG. 6
and 7, this upper transition portion 8 is a planar extension of the
platform 34, while in FIG. 2 this upper transition portion includes the
raised wall 35. As previously mentioned, the embodiment of FIG. 6 will
likely require the use of a bone filler material in the space directly
above the platform that is not covered by the extension member 42 when the
components are interconnected. FIG. 7 may also require such filler
material.
The lower transition surface 7 of the connecting portion 4 may typically
cross first axis "A." It may cross axis "A" substantially perpendicularly,
as shown in FIG. 6, or it may cross it at an angle as shown in FIGS. 7 and
8. Such angle may be between about 5 and 90 degrees, as desired.
Alternatively, the lower transition surface 7 may bne a curved surface
which crosses axis "A," as shown in FIG. 2.
This modular prosthesis system may include a plurality of base portions of
varying sizes and a plurality of stem extensions of varying sizes, such
that any one of the stem extensions can be selectively attached to any one
of the base portions. The plurality of stem extensions may be sized to
provide a plurality of different offsets "0" between the first and second
axes "A" and "B." This difference may suitably be a different radial
distance or radial offset "0" between axes "A" and "B," as desired. Also,
stem extensions 1 may be provided with various stem lengths "L" or various
diameters "D," as desired.
While this invention has been described in terms of various particularly
advantageous embodiments, those skilled in the art can appreciate that
modifications can be made without departing from the spirit and scope of
this invention.
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